The basic image-forming process of color silver halide photography comprises the exposure of a silver halide color photographic recording material to actinic radiation (such as light) and the manifestation of a useful image by wet chemical processing of the material. The fundamental steps of this wet processing include color development to reduce silver halide to silver and to produce dye images in exposed areas of the material.
To obtain useful color images, it is usually necessary to remove all of the silver from the photographic element after color development. This is sometimes known as “desilvering”. Removal of silver is generally accomplished by oxidizing the metallic silver in what is known as a “bleaching” step using a bleaching agent, and then dissolving the oxidized silver and undeveloped silver halide with a silver “solvent” or fixing agent in what is known as a “fixing” step.
It has become common for the processing of certain photographic elements, notably color photographic papers, to combine the bleaching and fixing operations into a single “bleach-fixing” operation that can be carried out in one or more processing steps. Bleach-fixing is usually carried out using a composition that includes both a photographic bleaching agent and a photographic fixing agent, as described for example in U.S. Pat. No. 4,033,771 (Borton et al.).
The most common bleaching agents for color photographic processing are complexes of ferric [Fe(III)] ion and various organic chelating ligands (such as aminopolycarboxylic acids), of which there are hundreds of possibilities, all with varying photographic bleaching abilities and biodegradability. Common organic chelating ligands used as part of bleaching agents for photographic color film processing include ethylenediaminetetraacetic acid (EDTA), 1,3-propylenediaminetetraacetic acid (PDTA) and nitrilotriacetic acid (NTA). Common color paper bleaching is often carried out using EDTA as a chelating ligand. Also known are bleaching, bleach-fixing compositions, and processing methods that utilize a ferric complex of one or more of several alkyliminodiacetic acids (such as methyliminodiacetic acid or MIDA) that are known to be more biodegradable than other common organic chelating ligands such as EDTA. Other photographic bleaching agents using similar organic chelating ligands are described in U.S. Pat. No. 5,061,608 (Foster et al.).
Typical photographic fixing agents include thiosulfates, sulfites, thiocyanates, and mixtures thereof that readily solubilize or “dissolve” silver ion in the processed photographic materials, as described for example in U.S. Pat. No. 5,633,124 (Schmittou et al.).
As pointed out in U.S. Pat. No. 5,055,382 (Long et al.), when photographic materials are processed in bleach-fixing steps, the bleach-fixing composition is generally formulated from two or more “parts”, each “part” or solution typically containing one or more (but not all) of the photochemicals necessary for the processing reactions. For example, one of the “parts” usually contains the conventional ferric bleaching agent, and another of the “parts” usually contains a thiosulfate fixing agent(s) and a sulfite preservative. These “parts” are sometimes provided together in a photochemical processing “kit”. If all of the chemicals are formulated in a single concentrate solution, storage stability is reduced or nonexistent since unwanted chemical interactions among components are inevitable. For example, ferric bleaching agents, sulfite preservatives, and thiosulfate fixing agents are inherently reactive, thereby degrading solution effectiveness and storage stability. Thus, most common bleach-fixing solutions are provided from “two parts”, each part containing at least one essential reactive component.
While most commercial bleach-fixing compositions satisfactorily remove silver from the processed photographic materials, sometimes a given set of processing conditions, processing compositions, and processed materials results in insufficient silver removal, especially in photographic color papers. This problem may be accentuated during “rapid” processing of the photographic color papers, for example, where the bleach-fixing time is less than 35 seconds. Moreover, the problem is more prominent when certain photographic color papers are rapidly processed, for example when color papers containing silver iodide, phenyl mercaptotetrazole, or block copolymers in the photographic emulsions are rapidly processed.
There is a need in the industry for the ability to rapidly process a variety of photographic color papers using bleach-fixing compositions that contain generally known components and that can be readily used under a variety of replenishing conditions.